Analog switch

Abstract

An analog switch having a first feedback amplifier supplied with a signal superposed with a bias voltage and a second feedback amplifier supplied with the bias voltage. Each amplifier has a differential amplifier formed of two symmetrically connected transistors and having an output connected to both a common output terminal and its input through an impedance transforming transistor. The differential amplifier is biased by a constant current source formed of a transistor and a diode. In the presence of a control signal, the first amplifier is closed through the normal operation of its constant current source while the second amplifier is opened by disabling its constant current source. In the absence of the control signal, the first and second amplifiers are opened and closed, respectively.

What we claim is: 
     
       1. An analog switch having first and second amplifiers, each of said amplifiers comprising: a pair of transistors connected in a common emitter differential amplifier configuration;   an active load for said differential amplifier, said active load formed of a diode and a transistor connected to the collectors of said differential transistor pair;   an impedance matching transistor connected to said differential transistor pair for impedance matching an output of said differential pair;   a current source comprising a diode and a transistor operatively connected to the common emitters of said differential transistor pair, the base of said current source transistor serving as a control input of its respective amplifier to control the operation thereof;   said analog switch further including an inverter amplifier connected to said control input of one of said first and second amplifiers and having a control input signal applied thereto, said control input signal also applied to the control input of the other of said first and second amplifier control inputs;   wherein one of said first and second amplifiers has a signal consisting of a combination of an input signal superimposed on a bias voltage applied to an input of its respective differential amplifier and said other of said first and second amplifiers having an input of its respective differential amplifier connected only to said bias voltage;   an output from each of said impedance transforming transistors are connectedtogether to form a combined output, wherein said control signal enables one of said first and second amplifiers to be operative when said other of said first and second amplifiers is inoperative and enables said other of said first and second amplifiers to be operative when said one of said first and second amplifiers is inoperative.   
     
     
       2. An analog switch comprising a first amplifier having an input having a signal consisting of the combination of an input signal superimposed on a bias voltage supplied thereto and responsive to a first control signal to perform a switching operation, and a second amplifier having an input consisting only of said bias voltage supplied thereto and responsive to a second control signal which is opposite in phase from said first control signal to perform a switching operation, said first and second amplifiers having respective outputs connected together wherein said first control signal enables said first amplifier to be operative when said second amplifier is inoperative and said second control signal enables said second amplifier to be operative when said first amplifier is inoperative; wherein said first and second amplifiers are of the feedback type;   and wherein each of said feedback type amplifiers comprises a first and a second transistor forming a differential amplifier, a third transistor for impedance-transforming an output from said differential amplifier, and a fourth transistor forming a constant current source for biasing said differential amplifier; and,   wherein said first and second control signals are respectively supplied to said fourth transistor of said first and second amplifiers at its respective base.